Bars, specifically billets or ingots, are transformed into their final size, shape, and section by means of an extrusion process that forces the material to flow through a shaped opening in a die, reducing and changing the section. One of the most common extrusion techniques involves the use of extrusion presses.
These presses are equipped with loaders that align the billet with the press-centre line and facilitate billet feeding into the container. The billet is pushed into the container by means of a pusher, without moving the container, operated by mechanisms housed in the loader or press.
Alternatively, the billet can be kept suspended between two elements (for example, between the ram and the die); in this case, it is the movement of the container that causes the billet to be fed into the container. The second operating mode is typical of the so-called “Front-Loading presses”. In these presses, loading precision—meaning the perfect alignment between the axis of the billet and the axis of the press—becomes a critical parameter for machine reliability.
In general, billets loaded into extrusion presses can consist of a single workpiece or multiple workpieces placed side by side, with the axes parallel. The length of the billets may also vary and depends on the specifications of the press and loader.
The state-of-the-art loaders come in different shapes and sizes and include single-arm, two-arm, and telescopic-arm loaders and two-arm loaders with one arm moving in the direction of the press axis. Document EP-B-428.989 describes the last type of loader (two arms including one mobile one).
This type of loader is unable to support ail billets to be loaded along their entire length, from the minimum to the maximum, during the loading operation without leaving billet segments unsupported.
Document U.S. Pat. No. 5,755,546 describes a single-arm loader equipped with a billet pusher. This billet pusher is moved by a chain that is, in turn, driven by a motor. The pusher pushes the billet into the container.
This type of known loader has several drawbacks including the fact that it is not able to adapt to every billet length usable with the extrusion press.
Another disadvantage of the known loaders is the length of their holding grippers; this length is required to grip the billet securely. The length of the holding grippers determines the length of the shortest billet that can be loaded into the press: the longer the holding grippers, the greater the minimum length of the billet. This is a serious disadvantage since today's markets also demand extrusion presses able to handle very short billets.
Another problem encountered with known loaders is the lack of a continuous and rigid support along the entire length of the billet in the section included between the holding grippers. This is particularly significant when the press is used to extrude simultaneously billets formed by multiple workpieces; this can lead to a misalignment between the different workpieces. In the case of front-loading presses, in particular, this lack of alignment during the extrusion process leads to limited reliability in the loading operation and may cause collisions or scraping damage between the billet and the container.